The present invention relates to a polymer for a chemically amplified resist and a resist composition using the same. The present invention provides a polymer represented by the Formula (1) and a chemically resist composition for deep ultraviolet light comprising the same, The chemically amplified resist composition comprising the polymer represented by the formula (1) of the present invention responds process and can embody a micro-paten of high resolution on a substrate.

(a) Field of the Invention
The present invention relates to a polymer for a chemically amplified resist and a resist composition comprising the same. More particularly, the present invention relates to a novel polymer that can be used for a chemically amplified resist composition that can form finer patterns on a substrate in a micro-lithography process suitable for micro-processing of semiconductors, using a mono wavelength as the light source for light exposure, and which improves post exposure delay (PED) stability and has high resistance against the heat produced by dry etching, and a resist composition using the same.
(b) Description of the Related Art
The resist composition is generally used in the preparations of large size integrated circuits (LSI) or in high resolution lithography. Recently, resist compositions with high resolution and high sensitivity have been required due to the densification of large size integrated circuits. Such embodiments of microcircuits in semiconductor integrated circuits generally proceed using a lithography process through which process the microcircuit is constructed by coating resist on a substrate, transcribing patterns on the substrate using a prepared photo mask, and etching the substrate along the transcribed pattern.
Such lithography processes comprise the following steps: (a) a coating step comprising uniformly coating resist on the surface of a substrate, (b) a soft baking step comprising evaporating the solvent from the coated resist film to adhere the resist film to the surface of the substrate, (c) a light exposure step comprising light exposing the substrate while projecting the circuit pattern on the mask, repeatedly and sequentially using a light source such as ultraviolet light to transcribe the pattern of the mask onto the substrate, (d) a development step comprising selectively removing the part in which chemical properties such as solubility change by the exposure to the light source using development liquid, (e) a hard baking step for adhering more firmly the resist film that remains on the substrate after development, (f) an etching step comprising etching the predetermined part along the pattern on the developed substrate in order to impart the electric properties and (g) a stripping step comprising removing the resist that becomes unnecessary after said etching step.
The speed of high-integration of semiconductor integrated circuits has increased 4-fold for 3 years. Thus, at present, in the field of dynamic random access memory (DRAM), 64 mega bit DRAM and 256 mega bit DRAM are mass-produced, and the development of giga bit DRAM has started.
The conventional 16 mega DRAM used the technology of a 0.5 xcexcm circuit line, while 64 mega DRAM uses the technology of a circuit line of 0.3 xcexcm or less, and 256 mega DRAM and giga DRAM requires an ultra micro pattern of less than quarter micro, such as 0.20 xcexcm, 0.18 xcexcm, 0.15 xcexcm depending on the design. In such micro-processing, the light-radiation wavelength moves to deep ultraviolet. Therefore, there is a need for the development of a new resist that can effectively respond to deep ultraviolet light.
The resist of the prior art comprising quinonediazide photoactive material and phenol novolac resin cannot satisfy the above-mentioned requirement, because, in such a resist system, there is a large absorption at the wavelength zone of 300 nm or less and thus, when mono wavelength light-exposure of 300 nm or less is conducted, pattern profile is significantly deteriorated. Therefore, there is a need for the embodiment of a stiff pattern in which the pattern profile does not flow.
In order to embody such a pattern profile, an aligner commonly called a stepper is generally used as a light-exposing apparatus. Such light-exposing apparatuses are divided into an apparatus using G ray (wavelength 436 nm), I ray (wavelength 365 nm) of mercury light, and an apparatus using an excimer laser of mono wavelength KrF (248 nm) and ArF (193 nm) according to the light source. For embodying micro-patterns on the substrate, the resolution value (R) should be small. The resolution value is expressed by the following Rayleigh diffraction limiting equation. Theoretically, since the resolution value becomes smaller as the wavelength of the light source becomes shorter, it is preferable to use a shorter mono wavelength.
[Diffraction limiting equation]
R=xcexaxcex/NA
Wherein, xcexa is a constant, xcex is a wavelength of the light used, and NA is the number of the aperture of the lens.
In order to achieve high resolution of a quarter micron or less, the capacity of degradation of lithography should be improved. For this purpose, it is effective to use a mono wavelength light source having a short wavelength and to increase the aperture number (NA) of the optical lens of the exposing apparatus.
Accordingly, a resist composition that uses a high-output excimer laser light source so as to respond to the high-resolution tendency of semiconductor integrated circuits is commonly used. This composition is for a KrF and an ArF excimer laser, and high-sensitivity resist systems introducing the chemical amplification concept are suggested.
A chemically amplified resist produces acid by photolysis due to the irradiation of ultraviolet light. The produced acid degrades the protective group which is partially protected with the aid of heat, and then it reacts with the acid labile polymer to initiate the chain reaction or act as a catalyst, and thus, one molecule of acid causes a number of bond formation or bond degradation reactions. Therefore, a term xe2x80x9cchemical amplificationxe2x80x9d means the phenomenon whereby active species produced by the action of one photon causes chemical chain reactions to rapidly amplify the yield of quantum. Due to this continuous reaction of acid, the concept of chemical amplification was introduced and used.
A chemically amplified resist is divided into a two-component system comprising an acid-labile polymer and a photo acid producing agent and a three-component system comprising an acid-labile polymer, a photo acid producing agent and a matrix resin. In the resist of the prior art, the degradation or the cross-reaction of a light sensitive material occurs directly at the light exposure part, and, when it is developed, a resist image pattern of a positive or negative form is obtained. However, in the chemically amplified resist, an acid labile polymer or compound is not directly reacted by light exposure, but an acid is produced from the photo acid producing agent in the light-exposed part, and only a latent image is produced. The produced acid acts as a catalyst for the acid labile polymer in the post-exposure bake (PEB) step, and thus, it causes the amplification of the reaction and the significant difference in solubility.
The first resist based upon the chemical amplification concept was a resist using a polyhydroxystyrene derivative poly[p-(t-butyloxycarbonyloxy)styrene] (PBOCSt) blocked with t-BOC (tertiary-butoxy carbonyl) group and onium salt as a photo acid producing agent, and it is described in American Chemical Society, xe2x80x9cPolymers in Electronicsxe2x80x9d, ACS Sym. Series, No. 242, by Ito et al. The reason for using the polyhydroxystyrene derivative is as follows: since the novolac phenol resin that was used in the resist of the prior art largely absorbs deep UV, UV light cannot sufficiently reach the contact surface of the resist substrate. Thus, in the light-exposed part of the resist, chemical changes by light-exposure do not sufficiently occur in the membrane thickness direction, and thus the solubility of the developing liquid becomes irregular. This makes the shape of the section of the resist pattern formed after development triangular. Thus, when the obtained resist pattern is used as an inner etching mask for a substrate, the micro-circuit pattern to be aimed cannot be transcribed. In order to compensate for this, there is a need to change the base polymer, and a polyhydroxystyrene derivative having excellent plasma resistance is known to be suitable.
As examples, a chemically amplified resist comprising poly(p-styreneoxytetrahydropyranol) and an acid producing agent is known by Ueno et al. In the 36th Japanese Applied Physics Society announcement, 1p-k-7, 1989, and a three component system resist comprising novolac phenol resin, bisphenol-A substituted with t-BOC group and pyrogallol methanesulfonic ester is known from Schlegel in the 37th Japanese Applied Physics Society announcement, 28p-ZE4, 1990. In addition, technologies relating to the preparations of said resists are disdosed in JP patent publication Hei. 2-27660, JP patent publication Hei. 5-232706, JP patent publication Hei. 5-249683, and U.S. Pat. Nos. 4,491,628 and 5,310,619. However, while such chemically amplified resists have excellent resolutions compared to the resist for G-ray and I-ray of the prior art, they are likely to be affected by the surrounding environment, particularly by oxygen, moisture and other trace ingredients around the membrane surface, and it is difficult to form stable micro patterns because a trace amount of acid is produced in the light-exposed part.
In addition, MacDonald et al. reported in Proc. SPIE, Vol. 1466. 1991 that trace dimethylanilline contained in the air decreases the activity of the acid produced around the surface of the resist by light exposure, and it produces a layer that hardly melts on the membrane surface, and said hardly-melting layer remains on the surface of the resist pattern after development treatment. However, this process has the problem that footing is caused by the reaction of the micro pattern with the substrate due to the time delay from the light exposure to the PEB process, and a T-top type pattern is produced by environmental pollution due to the amine ingredient distributed in the air in the process line. Therefore, there is a need for compensating the PED stability of the resist composition using said compound, and there is a need for a resist composition using a novel base polymer suitable to embody high sensitivity and high resolution at a wavelength of 300 xcexcm or less.
In addition, recently, large size integrated circuit tends to use a dry etching process. Said dry process is for increasing integration of semiconductor integrated circuit, and changes the manner of etching on the substrate in the lithography process from wet etching having large side etching of the prior art to dry etching having small side etching. In the dry etching process, the resist pattern should not change by the heat produced when etching. In addition, as the degree of integration increases, higher heat resistance is required by the resist used.
Accordingly, it is an object of the present invention to provide a novel polymer that can be applied to a chemically amplified resist composition that can form finer patterns on a substrate in a microlithography process using deep ultraviolet light, improves post exposure delay stability, and has high resistance against the heat produced by dry etching, and a resist composition using the same.
In order to achieve the above object the present invention provides a polymer for a chemically amplified resist represented by the following Formula 1.
Wherein, R1 is hydrogen or methyl, R2 is hydrogen or CH2CH2COOC(CH3)3, R3 is chloro, bromo, hydroxy, cyano, t-butoxy, CH2NH2, CONH2, CHxe2x95x90NH, CH(OH)NH2 or C(OH)xe2x95x90NH,
xe2x80x83x+y+z=1,x is 0.1-0.9,y is 0.01-0.89,z is 0.01-0.89,
and
n is 1 or 2, and when n is 2, both R2 are the same.
In addition, the present invention provides a resist composition comprising (a) a polymer represented by the formula 1, (b) an acid producing agent and (c) an organic solvent.
The present invention will now be explained in more detail.
In order to synthesize a polymer capable of being alkali developed 10 represented by the formula 1, three monomers constituting a polymer are prepared and they are introduced in a reactor equipped with a reflux cooler under a nitrogen environment and are reacted. Tetrahydrofuran (THF), toluene, benzene, chloroform, carbon tetrachloride, etc. can be used as a polymerization solvent. Azobisisobutyronitrile (AIBN) or benzoperoxide (BPO) can be used as a polymerization initiator. Said polymerization solvent and initiator are added to the reactor and reacted while being stirred. After the reaction completes, the synthesized polymer is precipitated in hexane to obtain precipitates, and then the precipitates rinsed several times and vacuum dried to obtain the polymer.
For synthesizing the monomer having a z repeat unit of the compound of Formula 1, the synthesis of cyanoalkylstyrene by way of Equation 1 should be preceded. To the synthesized 4-cyanoalkylstyrene, t-butyl acrylate and t-butyl methacrylate groups are added, and the prepared monomers are stirred with other monomers such as acetoxystyrene, t-butylacrylate, and t-butyl methacrylate to prepare the polymer.
The process for synthesizing the monomer having a z repeat unit comprises two steps. First, group I cyanide comprising sodium cyanide and s potassium cyanide is mixed with alkyl alcohol comprising water and ethanol, as shown in Equation 1. To said solution, alkyl styrene comprising 4-chloroalkistyrene and halogen atoms is slowly introduced and is reacted to synthesize cyanoalkylstyrene. Then, the monomer obtained in Equation 1 is stirred with t-butylacrylate to synthesize 4-(3cyano-di-1,5t-butoxycarbonyl-pentyl)styrene (CBCPS) as shown in Equation 2. Wherein, cyanoalkylstyrene and triton non-solution or tetraalkylaminehydroxide solution are dissolved in dioxane, and then, t-butylacrylate is introduced and stirred. After the reaction completes, said mixture is neutralized with an acidic solution and is extracted to synthesize CBCPS.
For the synthesis of the polymer of the present invention, THF, toluene, benzene, chloroform or carbon tetrachloride can be used as polymerization solvent. 4-acetoxystyrene or 4-butoxystyrene is added to the prepared CPCBS with 4-butylacrylate or 4-butylmethacrylate, and the polymerization initiator such as AIBN and BPO is added and the mixture is stirred to prepare a polymer. Said polymer has a weight average molecular weight (Mw) of 3,000-30,000, and the degree of dispersion can be controlled from 1.01 to 3.00 depending on the synthetic process.
The substitute monomer used in the present invention exhibits sufficient development inhibiting capacity at the non-light-exposed part, and the substitute group is degraded by the action of acid and is dissolved in developing liquid at the light-exposed part.
The resist composition using the polymer of the present invention comprises (a) a polymer represented by the formula 1, (b) an acid producing agent and (c) an organic solvent.
The resist composition using the polymer of the present invention preferably comprises 1-50 wt % of said polymer.
As the acid producing agent, sulfonium salt, an onium salt such as iodonium, N-iminosulfonate, disulfone, bisarylsulfonyldiazomethane and arylcarbonylarylsulfonyldiazomethane can be used. Preferably, the acid producing agent is contained in the resist composition in an amount of 0.1 to 50 wt %.
The examples of sulfonium salt include the following compounds but are not limited to them.
The examples of onlum salt include the following compounds.
The examples of N-iminosulfonates include the following compounds.
The examples of disulfones include the following compound.
(Wherein R is H, xe2x80x94CH3 or xe2x80x94(CH3)3.)
The examples of bisarylsulfonyldiazomethanes include the following compound.
(Wherein R is H, xe2x80x94CH3 or xe2x80x94C(CH3)3.)
The examples of arylcarbonylarylsulfonyidiazomethanes include the following compound.
(Wherein R is H, xe2x80x94CH3 or xe2x80x94C(CH3)3.)
The organic solvent is preferably selected from the group consisting of ethyleneglycol monoethylether acetate, propyleneglycol monoethylether acetate, ethylether acetate, n-butyl acetate, methyl isobutyl ketone, ethyl lactate, 3-ethoxy-ethylproplonate, 3-methoxy-methylpropionate, diglycol monoethylether, 2-heptanone, diacetone alcohol, xcex2-methoxyisobutyric acid methylester, propyleneglycol monoethylether, propyleneglycol monomethylpropionate, methyl lactate, butyl lactate, ethyl pyruvate, xcex3-butyrol lactone, and a mixture thereof. Preferably, the organic solvent is contained in the resist composition in an amount of 0.1 to 99 wt %.
The resist composition using the polymer of the present invention may comprise a dissolution inhibitor in order to improve the dissolution inhibition of the non-light-exposed part. The use of the dissolution inhibitor makes the difference of solubility of the light-exposed part and non-light-exposed part larger and contributes to the improvement of contrast. Such dissolution inhibiting additives can be added in the resist composition in an amount of 0.1 to 50 wt % based on the weight of the polymer of the present invention.
The examples of the dissolution inhibitor include the following compounds but are not limited to them.
(Wherein R is a molecule comprising C1-C10 and H and O)
The resist composition using the polymer of the present invention can be applied as follows to obtain a micro-pattern.
When the resist composition using the polymer of the present invention is formed as a thin layer on a substrate such as a silicone wafer and is treated with a base aqueous solution, the dissolution does not occur because the solubility of the copolymer is low. However, when deep ultraviolet light is radiated, the resist responds and the add producing agent in the resist produces acid, and the development inhibiting substituent causes the degradation of the polymer structure by the action of heat addition in the light-exposed part and the acid is produced again. Consequently, one acid that was produced causes chemical amplification which causes a plurality of acid active degradation. As a result, the solubility of the polymer largely increases in the light-exposed part, and, when developing with the base aqueous solution, the difference in the solubilities of the light exposed part and non-exposed part appears. Thus, a resist composition having excellent resolution compared to the resist composition using G-rays and I-rays of the prior art can be obtained.
The present invention will be explained in more detail with reference to the following Examples and Comparative Examples. However, these are to illustrate the present invention, and the present invention is not limited to them.
The Synthesis of 4-Cyanomethylstyrene(CyMS)
In a 500 xcexcl 4-opening flask equipped with a stirring bar, 49.01 g of sodium cyanide was mixed with 70.07 g of water and 50.96 g of ethanol. Then, the temperature of the flask was elevated to 60xc2x0 C. and the sodium cyanide was completely dissolved. To said solution; 87.50 g of 4-chloromethylstyrene was slowly added and it was reacted for 3 hours while stirring and maintaining the reaction temperature within 60-70xc2x0 C. When the reaction terminated, said solution was cooled to 40xc2x0 C., and 100 g of diethylether was added and the diethylether layer was separated. The separated organic layer was extracted with 300 g of water three times, and the water layer was extracted with 50 g of diethylether and was combined with said organic layer. The separated obtained organic layer was dried with magnesium sulfate for one day, and then the organic solvent was removed using an evaporator to obtain the product 4-cyanomethylstyrene. The yield of the product was 80%, and the product was a deep purple color.
Said synthesis was according to the Equation 1.
The Synthesis of 4(3-Cyano-di-1,5-t-butoxycarbonyl-pentyl)styrene (CBCPS)
In a 500 ml 4-opening flask equipped with a stirring bar, 57.28 g of 4-cyanomethylstyrene prepared in the above process and 1.4 g of triton non solution were dissolved in 40 g of dioxane. 102.54 g of t-butylacrylate were slowly added to said solution for 30 minutes while maintaining the temperature of the reactor at 60xc2x0 C., and it was reacted for 24 hours while stirring. After the reaction, the reactant was neutralized with a chloride solution, and the neutralized reactant was extracted with 100 g of diethylether and 300 g of water three times, the water layer was extracted with 50 g of diethylether and combined with the organic layer. The separated obtained organic layer was dried with magnesium sulfate for one day, and then the organic solvent was removed using an evaporator. The obtained product was distillated under reduced pressure to remove unreacted material, and it was recrystallized with methanol to obtain light yellow CBCPS in a 60% yield.
Said synthesis was according to the Equation 2.
The synthesis of the polymer of Formula 1
In a 500 ml 4-opening flask equipped with a temperature controlling apparatus and a nitrogen introducing apparatus, 300 ml of THF were introduced and nitrogen was purged and it was stirred for 30 minutes. To said reactor, 56.62 g of 4-acetoxystyrene, 9.16 g of t-butylacrylate and 24.14 g of CBCPS prepared in the above process were added, 1.21 g of AIBN was added and stirred for 30 minutes under a nitrogen atmosphere while maintaining the temperature at 40xc2x0 C., and the temperature of the reactor was then elevated and the reactant was stirred for 24 hours while refluxing. After the completion of the reaction, the temperature was lowered to room temperature and the reactant was deposited in 3 liters of hexane to obtain the precipitates. The obtained precipitates were filtered and rinsed with 2 liters of hexane several times and were vacuum dried. The dried macromolecule was dissolved in 300 ml of methanol in a flask, and 50 ml of 30% NH4OH aqueous solution were added and the mixture was slowly stirred, and, after the polymer was completely dissolved, the mixture was additionally stirred for 30 minutes. The solution was deposited in 1.5 liters of water to obtain the precipitates, and the precipitate were filtered and rinsed with 2 liters of pure water and vacuum dried to obtain 58.23 g of polymer of Formula 1.
The above synthesis was according to Equation 3.

Chemically amplified resist and a resist composition


The present invention is directed to a reagent composition for use in detection and quantification of glucose in urine comprising a first chromogenic indicator reagent combination capable of color development to indicate the presence of a lower concentration of glucose, a second chromogenic indicator reagent combination capable of color development to indicate the presence of a higher concentration of glucose, wherein the first chromogenic indicator prevents color development of the second chromogenic indicator unless the higher concentration of glucose is present, a scavenger that prevents color development of the first indicator reagent composition unless a threshold concentration of glucose is present.

The present invention relates to a dry chemistry test device for glucose detection in liquid samples. More particularly, the invention is directed to a test device for threshold detection and quantification of glucose in urine and to methods of making and using the same.
The detection of glucose levels is important in the treatment of diabetes. Test devices for glucose testing of the blood and urine of human diabetics, including many dry chemistry test devices or test strips, are described in numerous papers and patents. Glucose tests have been available in a dry test strip format for more than three decades. Analysis of blood and urine using test strips plays an important role in the diagnosis and treatment of human diabetes.
The history of dry chemistry disposable test-devices for glucose detection is summarized in U.S. Pat. Nos. 3,964,871 and 5,563,042. Quick and simple glucose determination in body fluids using dry chemistry test devices under field conditions is important for the early detection, diagnosis, and control of both human and animal diabetes. Key requirements for dry chemistry colorimetric tests are to detect glucose in a wide range of concentrations and to achieve easily discemable color distinctions at variously defined glucose levels.
For detection of relatively low glucose levels with test strips, several reagents have been proposed. U.S. Pat. No. 3,886,045 describes a non-toxic indicator comprising 4-aminoantipyrene and phenolic compounds that can form colored quinones in the presence of glucose. In U.S. Pat. No. 4,427,770, there is described a similar formulation using 4-aminoantipyrene, in a two pad test format to detect a wide range of glucose levels. U.S. Pat. No. 5,824,491 reports that 4-aminoantipyrene produces a gradual concentration/reflectance response from 0-400 mg/dL, with a linear concentration/reflectance response in the 150-400 mg/dL glucose range.
A sensitive and stable glucose test device was also described in U.S. Pat. No. 5,183,742. The test-device comprises a support having printed or coated detection reagent region on a surface. However, with only one peroxidatively active indicator, it proved difficult to obtain well discernable color changes over the broad range of 20-500 mg/dL.
Other indicator types have been used for detection and quantification of relatively high glucose levels and of a relatively wide range of glucose levels. In U.S. Pat. Nos. 4,303,753 and 4,340,669, an indicator in combination with a polymer (iodide+poly(vinylpyrrolidone)) is described for high range (500-1000 and 1000-10,000 mg/dL) glucose detection. Iodide salts have also been used in conjunction with a blue dye that fades in the presence of hydrogen peroxide. See, e.g., U.S. Pat. No. 3,814,668. The two components act in concert to provide a continuum of indicator colors.
A threshold color control system was described in U.S. Pat. No. 5,036,000. The system was designed for measurement of AND(P)H. Analytes react to form AND(P)H which is, in turn, oxidized by a chromogen. Non-chromogen competing compounds, such as Fe(III) compounds, are added to prevent a visible color change until a predetermined amount of AND(P)H is exceeded. When the predetermined amount of AND(P)H is exceeded, a single, easy to discern, color change is produced.
The above-mentioned reagents and test devices were generally designed for human urine testing. However, diabetes also afflicts animals. For example, feline diabetes is quite common, affecting about 0.2% to 1.0% of the cat population. In this affliction, glucose levels in the blood must be controlled. As with humans afflicted with diabetes, hyperglycemic cats are treated with insulin injections. While insulin treats the hyperglycemia, proper treatment of diabetes also requires periodic monitoring of glucose levels. Since elevated glucose levels in blood usually lead to elevated glucose levels in urine, periodic monitoring of glucose levels in the urine would provide needed screening for proper animal treatment.
While both the patent and non-patent literature is replete with reference to glucose testing systems and devices, few dry chemistry glucose tests have been developed specifically for testing the body fluids of animals. European Patent No. 0 060 133 describes a method and device for nonenzymatic glucose measurement in animal body fluids. Recently, a test strip product (Petstix(trademark) 7, Bayer Agricultural Division (Etobicoke, Ontario, Canada)) for animal urine testing (including glucose test) was introduced in the market. Petstix 7 uses the same color blocks as N-Multistix(trademark) SG (Bayer Diagnostics Division (Elkhart, Ind.)), which is marked with U.S. Pat. No. 3,814,668.
There are several limitations and specific requirements for animal urine testing with test strips. For example, there are salient compositional differences between cat urine and human urine. One such difference is that cat urine has a significantly higher specific gravity than does human urine. Because of this difference, false readings may be obtained ii test strips designed for human use are used for glucose detection in cats. Another limitation involves the problems in collecting a urine sample from the animal. In use with animal body fluids, it is also preferable to have a test device wherein the results are not dependent upon the amount of sample applied and the time of exposure to ambient conditions prior to activation, and wherein the results are stable for a prolonged period of time subsequent to activation.
The present invention is directed to a method, reagent composition, and dry chemistry test device for threshold glucose detection, particularly in cats. The device is in the form of an indicator impregnated substrate that is preferably cut into pieces suitable for being distributed onto cat litter. The indicator/substrate combination is selected so that after being wetted by animal urine, the indicator result remains discernable for a sufficient period of time to allow it to be observed by the pet owner or caretaker. Thus, the preferred indicator composition should not only be able to withstand the ambient conditions of a litter box and prolonged exposure to these conditions until activation by animal urine, but it should also have good stability even after activation with urine. The indicator reagent preferably should also be selected to indicate whether the reagent device has been contacted by animal urine, regardless of whether abnormal glucose levels are present.
The reagent composition used in the present invention is based on a standard glucose enzymatic system including glucose oxidase and peroxidase, and a combination of peroxidatively active indicators (chromogens). The combination of chromogens of the present invention provides for good color differentiation corresponding to a variety of urine glucose concentrations. Furthermore, glucose detection in cat urine is preferably based on an established sensitivity threshold or concentration threshold. At glucose concentrations less than the threshold, there would be no discernible color change on the test device. To achieve the desired sensitivity threshold, in addition to the combination of chromogens, the reagent composition includes a scavenger of peroxicle/oxidized chromogens. The reagent composition undergoes a color change only when exposed to urine having a glucose concentration at or above the threshold level, and, when such occurs, easily visually discernible color changes indicate higher glucose concentrations.
In one preferred embodiment the test device is prepared using a cellulose paper substrate impregnated with a solution of the reagent composition. The paper is then dried and cut into small but visually detectable pieces to provide a device that may be distributed on cat litter. The inactivated device remains glucose sensitive for several days even at high humidity. After contact with cat urine, a color indicative of glucose concentration develops and persists for a period of time sufficient to allow the pet caretaker to observe the color development. Color stability is achieved by incorporating stabilizers and selected chromogens into the reagent composition.
Thus, one aspect of the invention includes a dry chemistry device for glucose detection and quantification in urine, said device comprising a chromogenic indicator mixture comprising a first indicator capable of color development to indicate the presence of a low-to-medium concentration of glucose, and a second indicator capable of color development to indicate the presence of a higher concentration of glucose, wherein the first indicator also prevents color development of the second indicator unless the higher concentration of glucose is present in the urine, and a carrier impregnated with the chromogenic indicator mixture.
In a preferred embodiment of this invention, a scavenger is provided to prevent color development when the glucose concentration is below a threshold concentration. Therefore, another aspect of the invention is a device for detection and quantification of glucose in urine comprising a chromogenic indicator mixture comprising a first chromogenic indicator reagent combination capable of color development to indicate the presence of a lower concentration of glucose and a second chromogenic indicator reagent combination capable of color development to indicate the presence of a higher concentration of glucose, wherein the first chromogenic indicator prevents color development of the second chromogenic indicator unless the higher concentration of glucose is present, a scavenger that prevents color development of the first indicator reagent composition unless a threshold concentration of glucose is present, and a matrix impregnated with the chromogenic indicator mixture.
A third aspect of this invention is a method for determining urine glucose concentration in an animal comprising the steps of selecting a test device comprising a matrix impregnated with a chromogenic indicator mixture comprising a first chromogenic indicator reagent combination capable of color development to indicate the presence of a lower concentration of glucose and a second indicator reagent combination capable of color development to indicate the presence of a higher concentration of glucose, wherein the first chromogenic indicator reagent combination prevents color development of the second indicator unless the higher concentration of glucose is present, locating the test device to promote incidental contact of same with animal urine, reading a developed indicator color after the device has been wetted with urine, and comparing the developed color to a standard color chart and determining the animal""s urine glucose concentration.
Another aspect of this invention is a test kit for determining the concentration of glucose present in a sample of animal urine, the test kit comprising a substrate impregnated with a first chromogenic indicator reagent combination capable of color development to indicate the presence of a lower concentration of glucose, and a second chromogenic indicator reagent combination capable of color development to indicate the presence of a higher concentration of glucose, wherein the first chromogenic indicator prevents color development of the second chromogenic indicator unless the higher concentration of glucose is present in the urine sample; and a color chart indicating urine glucose concentrations corresponding to a plurality of discernible colors.
Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.
The present invention is directed to a method, reagent composition, and dry chemistry test device for glucose detection. While the invention is suitable for urine glucose detection generally, it is particularly suitable for urine glucose detection in cats. Preferably, the device is used for detection of glucose concentrations above a specific threshold level. In one preferred embodiment, the test device is formed as confetti-like material for use as a litter box additive. The problems presented by urine sample collection from cats and the relatively high specific gravity of cat urine present unique performance demands for the present test device relative to similar test strips used for testing of human diabetes.
The test device comprises an indicator mixture composition and a support matrix for the indicator composition. In a preferred embodiment, the support matrix comprises a piece of filter paper impregnated with the indicator composition, wherein the filter paper is of sufficient porosity and capillary affinity to allow an urinary sample from the animal to migrate into the matrix and interact with the indicator. The matrix may be a woven or a non-woven material and may include, but is not limited to, cellulosic natural fiber materials of the type normally used to make filter papers. Alternatively, organic polymer materials may be used. Other natural or synthetic fiber matrix materials, either woven or non-woven, may also be used.
It is preferable that the reagent indicator composition of the test device develop a threshold color response, wherein no discernible color change is produced unless the amount of glucose in the urine sample exceeds a predetermined concentration. Such would enable an animal owner or caretaker to observe the presence of a color change, indicating a possible hyperglycemic problem. Only if the threshold concentration were exceeded would the alerted caretaker need to investigate further to determine the severity of the hyperglycemic condition.
It is also preferable for the color differentiation to be strong enough to allow a reliable color detection and interpretation directly on the cat litter surface. Furthermore, the test device should remain glucose sensitive for at least several days, even at high humidity, after being applied on the cat litter surface. Additionally, the color signal of the urine activated device should be stable for at least several hours after exposure to cat urine. Other preferred features of the present test devices include that the color from the activated indicator reagent should not leach onto cat litter under conditions of normal use and observed test color should not depend on the amount of cat urine applied.
In one embodiment, the matrix impregnated with the indicator composition may be cut into small confetti-like pieces, to be sprinkled on or mixed into litter. The small pieces may be of various geometric shapes and typically 0.01 to 1.0 inches in its longest dimension, more typically, 0.1 to 0.5 inches in its longest dimension, and most typically squares or diamonds 0.2 inches on a side. However, it should be understood that the present invention is not limited for use with cats, and other shapes and sizes may be appropriate for human use or for use with other animals. For instance, much larger test sheets (1.0 to 20 inches in the longest dimension) may be suitable for use with paper-trained dogs. The larger sheets also may be placed under litter material in a cat litter box or under similar material for use with other animals. The test device may be sealed, for example in a foil package, to prolong product shelf life for distribution, sale, and use.
The reagents of the present invention are based on formulations having glucose oxidase, peroxidase, and chromogenic redox indicators as key components. Glucose is oxidized to gluconic acid by atmospheric oxygen in a specific glucose oxidase-catalyzed reaction that produces hydrogen peroxide as a byproduct proportional to the amount of glucose:
In various reactions catalyzed by peroxidase, hydrogen peroxide reacts with the colorless form of the indicator reagent composition to produce water and an oxidized, colored form of the indicator. The oxidized form of the indicator may itself be a colored entity or more typically reacts with another component to provide a colored product indicative of some concentration range. of glucose in the tested sample. In the indicator mixture of the present invention two different indicator reagents are used; one to detect low/medium glucose levels (Ind 1) via Reaction 1, and another to provide a different colored signal at high glucose levels (Ind 2) via Reaction 2.
Reaction 1 uses an indicator reagent composition (Ind 1) that has a relatively rapid susceptibility to oxidation by peroxidase. Thus, Reaction 1 has a high reaction rate as compared to Reaction 2. In the presence of low/medium glucose levels (preferably 150-300 mg/dL), a component of Ind 1 is oxidized and corresponding colors (for example rose or red when Ind 1 is AAP/HBS) are developed. The device detects low/medium glucose levels mainly on the basis of Reaction 1:
Suitable compositions for Ind 1 include 4-aminoantipyrene (AAP), or a salt thereof, and phenolic compounds, such as 2-hydroxy-3,5-dichlorobenzenesulfonate (HBS), 3-methylcatechol, 4-hydroxybenzenesulfonic acid, and 2,6-dimethylphenol. Other phenolic and aniline compounds capable of forming a colored compound with AAP are known in the art and are within the scope of this invention. See, for example, U.S. Pat. Nos. 3,886,045 and 4,427,770, hereby incorporated by reference. Other chromogenic aromatic compounds may be substituted for AAP. For example, 3-methylbenzothiazolinone hydrazone hydrochloride (MBTH) may be used. The combination of 1,3-phenylenediamine and MBTH produces an intense dull red color when activated with hydrogen peroxide.
In one embodiment of this invention, Ind 2 comprises an iodide salt. While potassium iodide is preferred, other iodide salts may be used, including but not limited to sodium iodide and ammonium iodide. The iodine that is released in Reaction 2 forms a colored complex with starch and other substances, as known in the art. See, for example, U.S. Pat. No. 3,886,045, hereby incorporated by reference. Substances capable of forming a colored complex with iodine include starch, starch components such as amylose or amylopectin, polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol. However, depending on the use, care must be taken in selecting a suitable substance, as some otherwise appropriate substances may be toxic. Because starch is relatively inexpensive, non-toxic, and provides good color, starch is preferred. Thus, Reaction 2 using iodide/starch is as follows:
In the absence of any other indicator, iodide/starch produces a characteristic blue color in the 50-300 mg/dL range, with increasing blue color with increased glucose concentration.
Reaction 2 has been observed to proceed more slowly than Reaction 1. In a preferred embodiment, the total stoichiometric amount of Ind 1 in the reagent composition is equal to, or slightly exceeds, a low/medium glucose level. In the presence of low/medium glucose levels, Ind 1 quickly consumes the available peroxide and Reaction 2 does not proceed. When AAP/phenol is used, the only color change observed at lower concentrations is due to AAP/phenol. A similar scavenging effect is seen with MBTH/1,3-phenylenediamine. At high glucose levels (preferably above 300 mg/dL) all of Ind 1 is consumed and Ind 2 interacts with H2O2/peroxidase. As a result, a color specific for Ind 2 (for example dark brown-black or dark blue when Ind 2 is starch/iodate) is developed. Thus, Ind 2 is used mainly to detect high glucose levels.
In a preferred embodiment, in addition to the double indicator composition described above, a scavenger is used to provide a threshold detection level for the device, wherein no color change is observed at glucose urine levels below the threshold concentration. In this preferred embodiment, a scavenger is used to prevent a color change at very low levels of glucose, as shown in Reaction 3:
In the presence of very low glucose levels (preferably less than 50 mg/dL) the colored (oxidized) form of Ind 1 may be produced. However, a scavenger may be selected so that under conditions of low glucose concentration, the scavenger reacts with oxidized Ind 1 and transforms it back to the colorless reduced form. Thus, in these conditions no color is developed and only the background coloration can be seen. Alternatively, a scavenger may be used that out competes the Ind 1 indicator for peroxide, preventing Reaction 1 from proceeding in low levels of glucose. In either case, predetermined amounts of the scavenger in the formulation correspond to a very low glucose level. In the presence of glucose levels greater than the capacity of the scavenger (preferably 50 mg/dL and more), the concentration of the oxidized Ind 1 exceeds the concentration of the scavenger, Ind 1 remains in its oxidized form, and glucose is detected. Depending on the application, suitable scavengers include stannous chloride, thiosulfates, and mercaptans. Because it is non toxic, a preferred scavenger is cysteine.
Urine from diabetic cats undergoing insulin therapy should have some residual urine glucose. Therefore, it is preferred that the test device indicate a level of 50 mg/dL, in order to detect or prevent an overdose. This threshold level may be varied for different animal or human applications.
The above-described combination of indicators and scavengers provides a threshold glucose detection, as well as various indicator colors in the low-high urine glucose concentration range associated with diabetes in cats. It should be stressed that the threshold color change may be shifted as needed for individual applications, particularly in the 50-1000 mg/dL glucose range. Appropriate amounts of Ind 1 and scavenger may be chosen to produce a threshold color and an Ind 1/Ind 2 color change at desirable glucose levels.
It is preferred that the test device have good stability and be able to withstand ambient conditions of a litter box and prolonged exposure of these conditions until its activation by being wetted with animal urine. Also, it is preferred that the resultant color produced upon activation by the animal urine remain unchanged for a significant period of time. In this regard, the scavenger (for example, cysteine) included in the reagent formulation plays a dual role. The scavenger not only facilitates color distinction between very low and low glucose levels, but it also provides an antioxidant function to protect the indicators from spontaneous oxidation during reagent preparation, storage, and application.
In a preferred embodiment of the invention, the reagent composition is formulated to contain a polysaccharide, such as Dextran, DEAE-Dextran, or Alginate, to improve enzyme stability and to maintain adequate test performance of the test device during prolonged exposure to ambient conditions on cat litter. Furthermore, a film-forming polymer, such as poly(vinyl alcohol), may be used in the reagent composition to aid in preventing the indicator from leaching from the reagent when activated with cat urine.


In telecommunications switching systems, software is frequently modified, enhanced or replaced altogether by new versions. The implementation or integration of the new or revised software into the operational system must be accomplished in accordance with strict requirements for not disturbing the ongoing activities of the system. Therefore, it is desirable that the system not be halted while the change to the new software is made. Rather, the preferred approach is to be able to replace software modules with new versions on the fly, during system operation. The smooth modification made possible in the disclosed system allows such changes with minimal disturbance to ongoing activities by dynamically linking and binding software modules during execution. The disclosed system accomplishes this by applying expanded object-oriented programming techniques and utilizing language-independent interface specifications that remain unchanged and that obviate the need for storing symbolic information that would be subject to change following modification.

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the patent and trademark office, patent file or records, but otherwise reserves all copyrights whatsoever.

System for dynamic run-time binding of software modules in a computer system


Applicant has developed an improved adsorbent useful in removing contaminants from various air streams. The adsorbent contains a zeolite, an alumina and a metal component. The metal component is present in an amount at least 10 mol-% of the stoichiometric amount of metal (expressed as the oxide) needed to balance the negative charge of the zeolite lattice. In a specific application an adsorbent comprising zeolite X, alumina and sodium is used to purify an air stream in order to remove water, carbon dioxide and other impurities including hydrocarbons.

This invention relates to the removal of carbon dioxide and other contaminants from gas streams, and more particularly to the pre-purification of air by the removal of contaminants from air prior to air separation. More specifically, the invention relates to adsorbents, having at least three components, that provide enhanced performance in the pre-purification of air.
Gases that occur in nature or which are produced in industrial processes often contain carbon dioxide in small amounts. Atmospheric air generally contains about 0.035% or 350 parts per million (ppm) carbon dioxide. It is sometimes desirable or necessary to remove the carbon dioxide from a gas because of certain process constraints or the intended end use for the gas. For example, air that is separated into various component products by cryogenic separation techniques (cryogenic air separation), such as cryogenic distillation or cryogenic adsorption, must be substantially free of both carbon dioxide and moisture. These operations are carried out at temperatures below the freezing points of water and carbon dioxide and consequently, if they are not removed, they will freeze and eventually clog the air separation process equipment.
Relatively pure oxygen (i.e. an oxygen-containing gas having an oxygen content of 88% or more) has a number of desirable industrial and medicinal applications at various pressures and purities. The Earth""s atmosphere, typically comprising nearly twenty-one percent oxygen gas, is the natural candidate for use as an economical oxygen source. Many of the most practical and economical oxygen production plants employ air separation systems and methods.
One of the more common systems for producing oxygen in relatively large volumes incorporates cryogenic technology to liquefy and separate a desired oxygen component of a predetermined purity from the air mixture. While the design works well for high-volume oxygen production, the specialized cryogenic hardware and associated high capital startup expenditures make such systems cost-prohibitive when used for production in low to moderate volumes, e.g. from about 30 to about 200 tons per day of an oxygen containing gas with an oxygen concentration higher than about 88% and up to about 95%.
Traditionally, higher volumes of oxygen have been produced via the well-known cryogenic rectification of air in which air is cooled to a temperature near the normal boiling point of the components and treated in fractionation columns. The significant capital and operating costs of the cryogenic separation systems are justified only when large quantities and/or extremely high purities (such as 97% to 99.999%) are required.
Before air can be introduced into a cryogenic air separation process in which oxygen and nitrogen are separated from one another, CO2 in the air at low levels must be removed in order to avoid the CO2 solidifying in the components of the air separation plant. Two methods generally used for such CO2 removal include temperature swing adsorption (TSA) and pressure swing adsorption (PSA).
In each of these techniques, a bed of adsorbent is exposed to a flow of feed air for a period of time to adsorb CO2 from the air. Thereafter, the flow of feed air is shut off from the adsorbent bed and the adsorbent is exposed to a flow of purge gas which strips the adsorbed CO2 from the adsorbent and regenerates it for further use. In TSA processes, the CO2 is driven off from the adsorbent by heating the adsorbent in the regeneration phase. In PSA processes, the pressure of the purge gas is lower than that of the feed gas and the change in pressure is used to remove the CO2 from the adsorbent.
Other components can be removed from the feed air by these processes, including hydrocarbons and water. These adsorption techniques can also be applied to feed gases other than air or be applied to air to be purified for purposes other than use in an air separation plant.
The choice of adsorbent is often the key to the effectiveness of the process. Much attention has been given to the development, improvement and manufacture of adsorbents, e.g. specialized zeolite adsorbents that have been synthesized through ion exchange, lower Si/Al containing structures and improved activation procedures. These additional and/or improved manufacturing steps have resulted in higher costs for these specialized adsorbents compared to standard adsorbents, e.g. LiX compared to 5A and 13X adsorbents in PSA air separation processes. In many processes the adsorbent has become a significant fraction of the overall capital investment. Thus, there is considerable incentive to reduce the cost of the adsorbent if such reduction can be transformed into an overall reduction in the cost of the desired product of the separation.
The prior art has attempted to address the problem of thermal cycling in PSA processes, in some instances by employing mixtures of materials. Mixtures have also been applied independent of thermal cycling effects to improve specific elements of adsorption process performance such as product purity or recovery or storage capacity. Distinct materials have been combined physically (co-mixture) in an adsorber or have been integrally bound in a single composite bead or pellet.
Mixtures of adsorbents have also been utilized when multiple separations are required. An example is provided in U.S. Pat. No. 4,194,892 A for the purification of steam reformer hydrogen involving the removal of carbon dioxide, methane and carbon monoxide using a rapid pressure swing adsorption (RPSA) process. It was shown that product H2 recovery was increased when a homogeneous mixture of activated carbon and crystalline molecular sieve was used in place of activated carbon alone.
In U.S. Pat. No. 5,779,767 A is described the use of an adsorbent mixture of a zeolite and an alumina to separate carbon dioxide, water and acetylene from a feed gas.
In U.S. Pat. No. 6,027,548 A is described a process for purifying a gas stream using a combination of a strong adsorbent such as NaX or NaY and a comparatively weak adsorbent, such as Al2O3. These adsorbents are used to separate relatively heavy components such as carbon dioxide from relatively light components, such as nitrogen.
Mixtures of fine and coarse particles have been applied to reduce interparticle void space, increase adsorbent density and increase gas storage capacity. EP 0 325 392 B1 (Kaplan et al.) provides an example of this methodology applied in PSA systems employing carbon molecular sieve (CMS) adsorbents for kinetic separation of air to produce N2. In Kaplan, the main CMS adsorbent is comprised of coarse particles (2.5 to 3.0 mm), while the void space between these larger particles is filled with fine particles of either an inert material or CMS adsorbent. The fine particle fraction is preferred to be an inert or non-adsorptive material (e.g. glass beads) and to occupy approximately 40% by volume of the adsorber bed. The reduction in void space was shown to improve process efficiency.
U.S. Pat. No. 4,499,208 A (Fuderer) doped activated carbon with inert dense alumina and achieved a reduced thermal swing when adsorbing C2 at high pressure from a feed stream containing H2, CO2, CO and CH4. Although the specific heat of the alumina is nearly the same as the activated carbon, the high density of the inert material significantly increases the heat capacity per unit volume of the bed. Lowering the thermal swing in the process significantly improved the process recovery.
The use of PSA for removing CO2 from air prior to separating air into its respective components by cryogenic air separation is described in numerous publications, e.g. U.S. Pat. Nos. 4,249,915 A and 4,477,264 A. Conventional processes employed a dual bed of alumina for water removal followed by a zeolite such as 13X for CO2 removal. More recently, all alumina PSA systems have been proposed, as described in U.S. Pat. No. 5,232,474 A. The advantages of an all alumina system include lower adsorbent cost, vessel design which does not need screens to separate the two different adsorbents and better thermal stability in the adsorption vessel during blow down and repressurization. However, alumina adsorbents have been less efficient towards NOx removal.
Alumina is also used as an adsorbent in TSA and for this purpose it has been proposed to treat the alumina to form alkali metal oxides thereon to increase the adsorptive capacity of the alumina. U.S. Pat. No. 4,493,715 A teaches a method for removing CO2 from olefin streams by contacting the feed gas with a regenerable, calcined adsorbent consisting of essentially from 1 to 6 wt-% of an alkali metal oxide selected from the group consisting of sodium, potassium and lithium on alumina. The adsorbent was prepared by contacting alumina with an alkali metal compound which is convertible to the metal oxide on calcination.
U.S. Pat. No. 4,433,981 A describes a process for removing CO2 from a gaseous stream which comprises contacting the gas stream at a temperature up to about 300xc2x0 C. with an adsorbent prepared by impregnation of a porous alumina with a sodium or potassium oxide. The corresponding oxide can be prepared by impregnation with a decomposable salt and calcining at a temperature of 350xc2x0 to 850xc2x0 C.
U.S. Pat. No. 3,557,025 A teaches a method for producing alkalized alumina which is capable of adsorbing SO2. The adsorbent is prepared by selectively calcining the alumina, and contacting with an alkali or ammonium bicarbonate salt to form at least 30% by weight alkalized alumina having the empirical formula of MAl(OH)2CO3.
Those skilled in the art continue to search for adsorbents suitable for use in PSA processes which provide improved CO2 adsorption capacity and which can be regenerated under PSA operating conditions. Moreover, those skilled in the art are searching for improved CO2 adsorbents which can be used in PSA processes which are integrated with other processes wherein adsorption of CO2 onto the adsorbent and regeneration of the adsorbent are accomplished at temperatures often substantially higher than ambient temperature.
Gas purification, more specifically air pre-purification, represents another class of adsorption separation processes where multiple adsorbents can be applied to improve process performance. The operation of cryogenic air separation plants requires large quantities of pretreated air. To prevent freezing and plugging of the primary heat exchanger, the concentration of contaminants such as CO2 and H2O must be lowered to less than 1 ppm with the typical specification for CO2 content of less than 0.1 ppm. In addition, the concentration of light hydrocarbons which have a low solubility in cryogenic liquids, such as acetylene, must be kept very low, typically less than 1 ppb, to prevent accumulation within the cryogenic distillation system. Currently both thermal swing adsorption (TSA) and pressure swing adsorption (PSA) are used in air prepurification applications.
TSA pre-purifiers use a relatively small amount of heated purge gas to regenerate the adsorption beds. The typical purge-to-feed ratio is 10 to 15%. TSA units are extremely effective at removing the major contaminants such as CO2, H2O and most of the hydrocarbons from an air feed because such adsorbers usually employ strong adsorbents. Any CO and H2 contained in the feed is generally carried over into the product. If it is necessary to remove the CO and H2, a sequential oxidation of the CO and H2 is carried out by catalytic conversion. The strong adsorbents used in TSA processes, such as 5A or 13X zeolite, require the large thermal driving forces available by TSA to affect adequate desorption. The operating adsorbate loadings and selectivities of the major contaminants on these strong adsorbents is such that CO2 breaks through into the product stream before acetylene and most other hydrocarbons that are harmful to cryogenic air separation plant operation, e.g., C3 through C8 hydrocarbons.
The feed gas is usually chilled to minimize the water content of the feed, which in turn reduces the amount of adsorbent required. This saves money by increasing the loading on a given quantity of adsorbent. While the TSA process results in a relatively low purge-to-feed ratio, the inherent heating of the purge and chilling of the feed adds to both the capital and operating cost of the process.
PSA pre-purifiers use a near-ambient temperature purge to regenerate the adsorption beds. The reduced driving force that is available from pressure swing alone requires a weaker adsorbent (e.g. alumina), shorter cycles and higher purge-to-feed ratios compared to TSA processes in order to achieve adequate desorption of H2O and CO2 contaminants. Typical purge-to-feed ratios are 40%-60% in PSA pre-purification.
The operating loadings of H2O on the weak adsorbents used in PSA may actually be larger than those for strong zeolites. Unfortunately, weak adsorbents such as activated alumina are unable to sufficiently retain light hydrocarbons such as acetylene in a reasonable size bed and C2H2 breaks through into the product stream ahead of CO2. This leads to a potentially hazardous operating condition in a cryogenic air separation process. While the capital costs associated with a PSA pre-purifier are lower than those of a TSA, the overall power requirement can be higher. In particular, blowdown or depressurization losses increase power consumption in the PSA pre-purifiers, i.e. PSA units cycle much faster than TSA units, resulting in an increase in the frequency of blowdown loss steps.
In light of the above considerations, there is a need in the pre-purification art for a PSA adsorbent bed that possesses the favorable desorption characteristics of activated alumina and yet has the acetylene selectivity and loading associated with the stronger zeolites. In addition, there is a need to minimize blowdown losses in order to reduce operating power. The prior art has attempted to address some of these problems.
DE 30 45 451 A1 (Hitachi), discloses a two bed adsorbent system. The first adsorbent (13X) is used to adsorb high concentrations of both H2O and CO2, thus suppressing the co-adsorption of nitrogen. The second adsorbent (activated alumina) does not co-adsorb nitrogen very strongly. The alumina is used to complete the H2O and CO2 adsorption. By minimizing the nitrogen co-adsorption in the beds, blowdown losses during depressurization are likewise minimized. Removal of light hydrocarbons was not addressed.
U.S. Pat. No. 5,232,474 A (Jain) uses a layer of activated alumina followed by a layer of 13X. Here it is claimed that the activated alumina layer is used to adsorb all the H2O and the majority of the CO2. The purpose of the downstream 13X layer is to remove hydrocarbons and residual CO2 from the gas stream. Jain teaches that the 13X layer is not intended to remove large amounts of CO2.
In addition to the prior art cited above that relates to bulk gas separation or air pre-purification processes, the prior art also offers several different methods of deployment of material mixtures, e.g. physically mixing at least two different materials, chemically bonding at least two different materials integrally in bead, pellet or granular form, and chemically bonding in preformed structures. Examples of simple physical mixtures of individual materials have already been cited above. The bonding of different materials in a single adsorbent particle or preformed structure typically involves steps of wet mixing, curing, drying and activation. The final composite product may perform better than the average of its individual components. This performance enhancement has not always been well understood, but such improvements have often been attributed to increased surface area and/or activity resulting from the have often been attributed to increased surface area and/or activity resulting from the processing of the mixture. In essence, these mixtures or composites represent a new adsorbent with improved physical properties.
It is therefore an object of the invention to provide a PSA system and process that reduces the cost of adsorption processes employing high performance, high cost adsorbents. This objective is supported by improving adsorbent efficiency and/or by reducing the cost of the adsorbent. Improved adsorbent efficiency means greater adsorbent effectiveness for the desired separation.
It is a further object of the invention to provide a safe, flexible PSA pre-purification process and system that ensures more efficient removal of contaminants with a lesser power requirement as compared to existing prior art systems.
Applicant has developed an improved adsorbent which can remove multiple contaminants from various streams. Surprisingly these contaminants can be removed with only a small temperature rise and the adsorbent has increased stability upon multiple regenerations. This adsorbent comprises a zeolite, alumina and a metal component which is present in an amount of at least 10 mol-% of the stoichiometric amount of metal (expressed as the oxide) needed to compensate for the negative charge of the zeolite lattice.
This invention relates to a solid shaped adsorbent, a process for preparing the adsorbent and a process for removing contaminants from an air stream using the adsorbent.
The present invention relates to a process for removing contaminants from streams comprising contacting the stream with a solid shaped adsorbent, at adsorption conditions to remove at least a portion of at least one contaminant, the adsorbent comprising an alumina component, a zeolite component and a metal component, the metal component present in an amount at least 10 mol-% of the stoichiometric amount of metal needed to compensate for the negative lattice charge of the zeolite expressed as the oxide.
These and other objects and embodiments will become clearer after the following detailed description of the invention.
The present invention comprises a solid shaped adsorbent, a process for preparing the adsorbent and purification processes using the adsorbent. With regard to the solid shaped adsorbent, one necessary component is an activated alumina. Activated aluminas include aluminas having a surface area usually greater than 100 m2/g and typically in the range of 100 to 400 m2/g. The activated alumina powder is preferably obtained by rapid dehydration of aluminum hydroxides, e.g., alumina trihydrate of hydrargillite in a stream of hot gases or solid heat carrier. Dehydration may be accomplished in any suitable apparatus using the stream of hot gases or solid heat carrier. Generally, the time for heating or contacting with the hot gases is a very short period of time, typically from a fraction of a second to 4 or 5 seconds. Normally, the temperature of the gases varies between 400xc2x0 and 1000xc2x0 C. The process is commonly referred to as flash calcination and is disclosed, for example in U.S. Pat. No. 2,915,365 A, incorporated herein by reference. However, other methods of calcination may be employed.
The activated aluminas suitable for use in the present invention have a median particle size in the range of 0.1 to 300 microns, preferably 1 to 100 microns and typically 1 to 20 microns. In certain instances, it may be desirable to use aluminas with a median particle size of 1 to 10 microns. The alumina may be ground to the desired particle size before or after activation. The activated alumina typically has an LOI (loss on ignition) in the range of about 5 to 12% at a temperature of 200xc2x0 to 1000xc2x0 C.
One source of activated alumina is gibbsite which is one form of alumina hydrate derived from bauxite using the Bayer process. However, alpha alumina monohydrate, pseudoboehmite or the alumina trihydrate may be used if sufficiently calcined. Other sources of alumina may also be utilized including clays and alumina alkoxides.
Another necessary component of the present invention is a zeolite. Zeolites are crystalline aluminosilicate compositions which are microporous and which have a three-dimensional oxide framework formed from corner sharing AlO2 and SiO2 tetrahedra. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. The zeolites which can be used in the present invention are those which have a pore opening of about 5 to about 10 xc3x85.
In general, the zeolites have a composition represented by the empirical formula:
M2/nO:Al2O3:b SiO2
M is a cation having a valence of xe2x80x9cnxe2x80x9d and xe2x80x9cbxe2x80x9d has a value of about 2 to about 500. Preferred zeolites are those that have a SiO2/Al2O3 ratio of about 2:1 to about 6:1 and/or those having the crystal structure of zeolite X, faujasite, zeolite Y, zeolite A, mordenite, beta and ferrierite. Especially preferred zeolites are zeolites X, Y and A.
Preparation of these zeolites is well known in the art and involves forming a reaction mixture composed of reactive sources of the components which mixture is then hydrothermally reacted to form the zeolite. Specifically, the synthesis of zeolite Y is described in U.S. Pat. Nos. 3,130,007 A and 4,503,023 A and that of zeolite X in U.S. Pat. Nos. 2,882,244 A and 3,862,900 A, the disclosures of which are incorporated by reference.
Although the synthesis of zeolites, and zeolites X and Y in particular, are well known, a brief description will be presented here for completeness. Reactive sources of M include the halide and hydroxide compounds of alkali or alkaline earth metals such as sodium chloride, sodium hydroxide, potassium hydroxide, etc. Aluminum sources include but are not limited to boehmite alumina, gamma alumina and soluble aluminates such as sodium aluminate or tetraethylammonium aluminates. Finally, silicon sources include, silica, silica hydrosol, silicic acid, etc.
The reactive sources are combined into a reaction mixture which has a composition in terms of mole ratios of the oxides of:
SiO2/Al2O3=8:12
M2O/Al2O3=2.5:4
H2O/M2O=120:180
and the mixture is then reacted to form the zeolite.
As synthesized, the zeolites will contain xe2x80x9cMxe2x80x9d metals in the channels and/or pores. The function of these metal cations is to balance the negative charge of the zeolite lattice. Since these cations are not part of the framework, they are exchangeable and are said to occupy exchange sites. The amount of metal cations present in the zeolite is referred to as the stoichiometric amount or the maximum ion exchange capacity of the zeolite. This amount is usually expressed in moles.
Since the metal cations initially present in the zeolite are exchangeable they can be exchanged for other (different) alkali metals, alkaline earth metals, hydronium ions, ammonium ions or mixtures thereof. If the zeolite to be used contains partially or completely hydronium or ammonium ions, then these ions must be fully exchanged with alkali metals, alkaline earth metals or mixtures thereof, either before or during the preparation of the composite adsorbent.
Another necessary component of the shaped adsorbent of this invention is a metal component selected from the group consisting of alkali, alkaline earth metals and mixtures thereof. This metal component is in addition to the metal cation (M) present in the exchange sites of the zeolite. Additionally, the metal can be the same or different than the (M) metal. For example, the metal component in a zeolite can be potassium whereas the metal can be sodium.
Specific examples include but are not limited to sodium, potassium, lithium, rubidium, cesium, calcium, strontium, magnesium, barium, zinc and copper. The source of the metal component (metal component precursor) can be any compound which at activation conditions, (see infra) decomposes to the metal oxide. Examples of these sources are the nitrates, hydroxides, carboxylates, carbonates and oxides of the metals. The shaped adsorbent can be prepared by combining the three components in any order and forming into a shaped article although not necessarily with equivalent results.
In one method, the alumina, zeolite and an aqueous solution of the desired metal compound are mixed and formed into a shaped article. For example, gamma alumina, zeolite X and a solution of sodium acetate can be combined into a dough and then extruded or formed into shapes such as pellets, pills, tablets or spheres (e.g. by the oil drop method) by means well known in the art. A preferred method of forming substantially rounded shapes or bodies involves the use of a pan nodulizer. This technique uses a rotating pan or pan nodulizer onto which is fed the alumina component, zeolite component and a solution of the metal component thereby forming substantially rounded articles or bodies.
Another method of forming the shaped article is to mix powders of the alumina, zeolite and metal compound followed by formation of pellets, pills, etc. A third method is to combine the alumina and zeolite components (powders), form them into a shaped article and then impregnate the shaped article with an aqueous solution of the metal compound. The forming step is carried out by any of the means enumerated above.
In preparing a solution of the desired metal compound, it is preferred to adjust the pH to a value from about 7 to about 14, more preferably from about 12 to about 14 and most preferably from about 12.7 to about 13.8. The pH of the solution is controlled by adding the appropriate amount of the desired metal hydroxide. For example, if sodium is the desired metal, sodium acetate can be used to form the aqueous solution and the pH is then adjusted using sodium hydroxide.
Having obtained the shaped articles, they are cured or dried at ambient temperature up to about 200xc2x0 C. for a time of about 5 minutes to about 25 hours. The shaped articles can be cured in batches e.g. bins or trays or in a continuous process using a moving belt. Once the shaped articles are cured, they are activated by heating the cured articles at a temperature of about 275xc2x0 to about 600xc2x0 C. for a time of about 5 to about 70 minutes. The heating can be done with the articles in a moving pan or in a moving belt where the articles are fired to provide the finished solid adsorbent.
The relative amount of the three components can vary considerably over a wide range. Usually the amount of alumina varies from about 40 to about 90% of the adsorbent and the amount of zeolite varies from about 5 to about 55 wt-% of the adsorbent. The amount of metal component can also vary considerably, but must be present in an amount equal to at least 10% of the stoichiometric amount of the metal cation, M, present in the exchange sites of the zeolite. For practical reasons, the maximum amount of the metal component should be no more than 50% of the stoichiometric amount of M. In absolute terms, it is preferred that the amount of metal component be present from about 0.015 to about 0.08 gram moles of metal per 100 gm of adsorbent. The amounts of metal are reported or expressed as the oxide of the metal, e.g. Na2O.
The streams are purified by contacting the stream with the solid adsorbent at adsorption conditions. The contacting can be carried out in a batch or continuous process with continuous, being preferred. The adsorbent can be present as a fixed bed, moving bed or radial flow bed with fixed bed being preferred. When a fixed bed is used, the feed stream can be flowed in an upflow or downflow direction, with upflow being generally preferred. If a moving bed is used, the feed stream flow can be either co-current or counter-current. Further, when a fixed bed is used, multiple beds can be used and can be placed in one or more reactor vessel. Adsorption conditions include a temperature of about ambient to about 80xc2x0 C. and a pressure of about atmospheric to about 100 atm. (1.01xc3x97104 kPa). The gas hourly space velocity varies from about 500 to about 10,000 hrxe2x88x921.
After a certain amount of time, which time depends on the concentration of contaminants, the size of the bed and the space velocity, the adsorbent will be substantially spent, i.e. has adsorbed an amount of contaminant(s) such that the level of contaminant in the purified stream is above an acceptable level. At this time, the adsorbent is regenerated. The spent adsorbent can be regenerated by means well known in the art and then placed back on service. Other variations of a PSA process or combination with TSA or vacuum swing adsorption processes may be employed as found to be useful in the practice of the present invention.

Composite adsorbents for air purification